Although frequency is widely recognized as a key predictor of vocabulary learning, relatively few studies have examined how lexical frequency shapes different dimensions of word knowledge under the condition of explicit vocabulary instruction. To address this gap, the present study investigated how high- and low-frequency words responded to identical post-reading explicit instruction. The study was original in that it: (a) treated lexical frequency, not exposure frequency, as the central variable, (b) held time-on-task, input, and instructional procedures constant to isolate its effects, and (c) drew on the connection between lexical frequency and different dimensions of word knowledge. Forty pre-intermediate EFL learners (N = 40) were assigned to either a high-frequency or low-frequency condition and received explicit instruction on 13 target words following a shared reading passage. Learners completed a 10-minute reading phase, a single 45-minute instructional session, and pre-tests, immediate post-tests, and delayed post-tests measuring form recall, meaning recall, and meaning recognition. Results showed that explicit post-reading instruction led to substantial gains in recall-based knowledge, with form recall emerging as the strongest dimension and meaning recognition the weakest. High-frequency words yielded consistently higher scores than low-frequency words, particularly in recall measures, whereas recognition scores showed no significant differences between frequency levels when exposure was controlled. These findings suggest that lexical frequency exerts its strongest influence on recall-based knowledge under explicit conditions, while recognition is less responsive to frequency when exposure and instructional conditions are strictly controlled.